As a conventional method for producing metal powder, there are a water atomizing method, which obtains metal powder by injecting a high pressure water jet to a flow of a molten material, a gas atomizing method which uses N2 gas or Ar gas in place of the water jet in the water atomizing method, and a centrifugation method which injects a molten metal jet into cooling water in a rotary drum rotating at high speed. Fine particles are also produced by a breakdown method such as mechanical fragmentation using a mill or the like and further by a buildup method such as a precipitation method or a sol-gel method.
However, in the water atomizing method and the gas atomizing method, structure of a nozzle should be complicated and a burden is imposed on the nozzle, resulting in making the nozzle worse in terms of durability since the molten metal can be fragmented into powder form by a flow of high pressure cooling water or cooling gas. On the other hand, in the centrifugation method, the structure of the apparatus is complicated because of the high-speed rotation of the rotary drum. Furthermore, all of the methods crush the molten metal using collision energy, and there occurs dispersion in the fragmentation and the fine particles cannot be formed with good yield.
The breakdown method using mechanical fragmentation or the like can produce only large particles up to, for example, approximately 100 μm. The buildup method such as a precipitation method can produce fine particles up to approximately 1 μm, and particles which are larger than that cannot be obtained. Therefore, it is difficult to obtain fine particles having the size ranging from several micrometer order to 10 μm order, particularly about 3 μm order in the conventional method as well as the apparatus for producing the fine particles.
Also, in the breakdown method, the percentage of the molten metal not being turned into fine particles and left as a lump is large. Therefore, a good yield of fine particles cannot be obtained. In addition, the particle size distribution is scattered and fine particles with desired particle diameter can not be obtained in large amount.
It is an objective of the present invention to provide a method and an apparatus which can produce fine particles of a metal or the like, the method being a simple method and the apparatus having a simple structure. Furthermore, the present invention enables easy production of fine particles having a size of submicrometer order to 100 μm order which cannot be realized in the previous method and apparatus. Moreover, it is another objective of the present invention to develop a method and apparatus for producing fine particles having desired particle diameter with good yield and an excellent extraction rate.